This invention relates generally to filtration apparatus and, more particularly to a filtration device utilizing a disposable stirred cell.
Filtration of low to moderate (1 ml to 1 liter) volumes of fluids are frequently done using a family of devices known as stirred cells. These devices require the user to install a disc of filtration material in a base and secure the disc in place with an "O" ring or comparable sealing mechanism. The user must then further assemble this device onto a column used to hold and pressurize the liquid sample, place a magnetic stir bar and pressure head on top of the column, and then place the entire device within a pressure clamp or shell. In turn the device (or shell, depending on the particular design) must be secured to an apparatus known as a stir plate. This is usually done with adhesive or masking tape. A typical stirred cell is disclosed in U.S. Pat. No. 3,539,155.
The above described operating procedure involves several problems in addition to the aggravation of assembly. These problems include:
(1) Orientation and location of the filter disc is a problem. Several types of filters commonly used in stirred cells are assymetric, and proper orientation is a critical factor. Sealing characteristics of "O" rings are not always good and leaky assemblies are a frequent problem, necessitating rinsing, disassembly and reassembly.
(2) If the user wishes to retain the liquid in the device he must transfer it to another vessel, as there is no proper cap for the stir vessel. In addition, using the stir vessel to store liquids would tie up a valuable piece of apparatus.
(3) Securing the pressure shell to the stir plate is awkward. There is no proper provision for quick and simple location and removal.
(4) Once together it is not at all obvious what porosity membrane is assembled in the stirred cell.
The object of this invention, therefore, is to provide an improved, more efficient stirred cell filtration device.